This invention relates to the field of automobile inflatable safety systems and more particularly to propellants for hybrid inflators.
U.S. Pat. Nos. 5,602,361 and 5,616,883 describe hybrid inflators for automobile inflatable safety systems which mix gases generated by a burning gun-type solid propellant with a compressed mixture of an inert gas (e.g., argon) and oxygen and use the resulting mixture to inflate an air/safety bag. Carbon monoxide (CO) and hydrogen (H.sub.2) in the propellant gases are converted by the oxygen to carbon dioxide (CO.sub.2) and water (H.sub.2 O). The burning of the gun-type propellant and the oxidation of the CO.sub.2 and H.sub.2 provide heat which drives the expansion of the compressed gases to inflate the bag. The gases which inflate the bag are nontoxic and do not obstruct the view of the people in the vehicle. The hybrid inflator system is compact, efficient, and safe.
A critical requirement of any air/safety bag system is that it must have a long shelf life. In other words, years later the system should work with no decrease in efficiency. U.S. Pat. Nos. 5,602,361 and 5,616,883 disclose the use of conventional solid gun-type propellants in the hybrid inflator systems. These conventional gun-type propellants contain low molecular weight plasticizers which over time migrate in the propellants, changing their properties. It would be desirable to provide a solid propellant with more consistent long term properties and thus a longer shelf life for the hybrid inflators. Such new propellants must not produce gases that are toxic or which obstruct the view of occupants of the vehicle. The new propellant must also have good, strong physical properties which make them suitable for use in a vehicle where they will be subject to many physical bumps and shocks.